Discovery and optimization of 4-oxo-2-thioxo-thiazolidinones as NOD-like receptor (NLR) family, pyrin domain-containing protein 3 (NLRP3) inhibitors

A small-molecule degron with a phenylpropionic acid scaffold

Targeted protein degradation (TPD), employing proteolysis-targeting chimeras (PROTACs) composed of ligands for both a target protein and ubiquitin ligase (E3) to redirect the ubiquitin-proteasome system (UPS) to the target protein, has emerged as a promising strategy in drug discovery. However, despite the vast number of E3 ligases, the repertoire of E3 ligands utilized in PROTACs remains limited. Here, we report the discovery of a small-molecule degron with a phenylpropionic acid skeleton, derived from a known ligand of S-phase kinase-interacting protein 2 (Skp2), an E3 ligase. We used this degron to design PROTACs inducing proteasomal degradation of HaloTag-fused proteins, and identified key structural relationships. Surprisingly, our mechanistic studies excluded the involvement of Skp2, suggesting that this degron recruits other protein(s) within the UPS.

Targeting NLRP3 Inflammasome: Structure, Function, and Inhibitors

Inflammasomes are multimeric protein complexes that can detect various physiological stimuli and danger signals. As a result, they perform a crucial function in the innate immune response. The NLRP3 inflammasome, as a vital constituent of the inflammasome family, is significant in defending against pathogen invasion and preserving cellhomeostasis. NLRP3 inflammasome dysregulation is connected to various pathological conditions, including inflammatory diseases, cancer, and cardiovascular and neurodegenerative diseases. This profile makes NLRP3 an applicable target for treating related diseases, and therefore, there are rising NLRP3 inhibitors disclosed for therapy. Herein, we summarized the updated advances in the structure, function, and inhibitors of NLRP3 inflammasome. Moreover, we aimed to provide an overview of the existing products and future directions for drug research and development.

Medicinal chemistry strategies targeting NLRP3 inflammasome pathway: A recent update from 2019 to mid-2023

Nod-like receptor protein 3 (NLRP3), a therapeutic target that has a close relationship with inflammatory diseases, has drawn significant attention from researchers in the field. An increasing number of NLRP3 inhibitors have been reported since NLRP3 was identified as a biomarker and inflammatory therapeutic target. Inhibiting NLRP3 has been widely studied as therapeutics for the treatment of cryopyrin associated periodic syndrome (CAPS), inflammatory bowel disease (IBD), nonalcoholic steatohepatitis (NASH), arthrolithiasis, Alzheimer's disease (AD) and Parkinson's disease (PD). This review updates the recently reported (2019 to mid-2023) molecule inhibitors targeting the NLRP3 inflammasome pathway, summarizes their structure-activity relationships (SARs), and discusses the therapeutic effects on inflammatory diseases. I hope this review will contribute to the development of novel inhibitors targeting NLRP3 inflammasome pathway as potential drugs.

Recent Progress and Prospects of Small Molecules for NLRP3 Inflammasome Inhibition

NLRP3 inflammasome is a multiprotein complex involved in host immune response─which exerts various biological effects by mediating the maturation and secretion of IL-1β and IL-18─and pyroptosis. However, its aberrant activation could cause amplification of inflammatory effects, thereby triggering a range of ailments, including Alzheimer's disease, Parkinson's disease, rheumatoid arthritis, gout, type 2 diabetes mellitus, and cancer. For the past few years, as an attractive anti-inflammatory target, NLRP3-targeting small-molecule inhibitors have been widely reported by both the academic and the industrial communities. In order to deeply understand the advancement of NLRP3 inflammasome inhibitors, we provide comprehensive insights and commentary on drugs currently under clinical investigation, as well as other NLRP3 inflammasome inhibitors from a chemical structure point of view, with an aim to provide new insights for the further development of clinical drugs for NLRP3 inflammasome-mediated diseases.

Small molecule inhibitors of NLRP3 inflammasome and GSK-3β in the management of traumatic brain injury: A review

Traumatic brain injury (TBI) is a debilitating mental condition which causes physical disability and morbidity worldwide. TBI may damage the brain by direct injury that subsequently triggers a series of neuroinflammatory events. The activation of NLRP3 inflammasome and dysregulated host immune system has been documented in various neurological disorders such as TBI, ischemic stroke and multiple sclerosis. The activation of NLRP3 post-TBI increases the production of pro-inflammatory cytokines and caspase-1, which are major drivers of neuroinflammation and apoptosis. Similarly, GSK-3β regulates apoptosis through tyrosine kinase and canonical Wnt signalling pathways. Thus, therapeutic targeting of NLRP3 inflammasome and GSK-3β has emerged as promising strategies for regulating the post-TBI neuroinflammation and neurobehavioral disturbances. In this review, we discuss the identification & development of several structurally diverse and pharmacologically interesting small molecule inhibitors for targeting the NLRP3 inflammasome and GSK-3β in the management of TBI.

Chlorogenic acid ameliorates Klebsiella pneumoniae-induced pneumonia in immunosuppressed mice via inhibiting the activation of NLRP3 inflammasomes

Chlorogenic acid (CGA) possesses a wide variety of bioactive properties, such as antioxidation, anti-inflammation and anti-bacteria. This study was aimed at exploring the effects of CGA of anti-inflammation and anti-bacteria on mouse pneumonia prepared by immunosuppressed mice infected with Klebsiella pneumoniae (K. pneumoniae) in vivo and the cellular inflammasomes through lipopolysaccharide (LPS) and adenosine triphosphate (ATP)-induced RAW 264.7 murine macrophages in vitro. Mice received CGA treatment (30 and 90 mg kg^-1) for 8 consecutive days and on the fourth day immunosuppression in mice was induced by cyclophosphamide (40 mg kg^-1) for 5 days before inoculation of K. pneumoniae. Immunosuppressed mice infected with K. pneumoniae developed severe pneumonia, with marked interstitial vascular congestion, widened alveolar intervals, infiltration of monocytes, lymphocytes and macrophages as well as the damage of epithelial architecture, with growing mortality and count forming unit (CFU). CGA treatment significantly decreased the ratio of lung/body weight, reduced the severity of pneumonia induced by K. pneumoniae, decreased the lung injury, inflammatory cell infiltration scores and CD68 protein expression, inhibited the expression of interleukin (IL)-6, IL-8, tumor necrosis factor (TNF)-α, and elevated the expression of IL-10. Meanwhile, we investigated the mechanism of CGA to counter K. pneumoniae-induced pneumonia and found that CGA remarkably repressed the activation of nucleotide-binding domain like receptor protein 3 (NLRP3) inflammasome. Altogether, our results indicate that the dietary intake of CGA or its rich foods ameliorates K. pneumonia-induced pneumonia by inhibiting the activation of NLRP3 inflammasomes.

Small molecule approaches to treat autoimmune and inflammatory diseases (Part II): Nucleic acid sensing antagonists and inhibitors

Nucleic acid sensing pathways play an important role in the innate immune system, protecting hosts against infections. However, a large body of evidence supports a close association between aberrant activation of those pathways and autoimmune and inflammatory diseases. Part II of the digest series on small molecule approaches to autoimmune and inflammatory diseases concentrates on recent advances with respect to small molecule antagonists or inhibitors of the nucleic acid sensing pathways, including endosomal TLRs, NLRP3 inflammasome and cGAS-STING.

Recent insights into the regulatory networks of NLRP3 inflammasome activation

The NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome is a fascinating cellular machinery endowed with the capacity for rapid proteolytic processing of the pro-inflammatory cytokine IL-1β and the cell death effector gasdermin D (GSDMD). Although its activity is essential to fight infection and support tissue homeostasis, the inflammasome complex, which consists of the danger sensor NLRP3, the adaptor apoptosis-associated speck-like protein containing a CARD (ASC; also known as PYCARD), caspase-1 and probably other regulatory proteins, also bears considerable potential for detrimental inflammation, as observed in human conditions such as gout, heart attack, stroke and Alzheimer's disease. Thus, multi-layered regulatory networks are required to ensure the fine balance between rapid responsiveness versus erroneous activation (sufficient and temporally restricted versus excessive and chronic activity) of the inflammasome. These involve multiple activation, secretion and cell death pathways, as well as modulation of the subcellular localization of NLRP3, and its structure and activity, owing to post-translational modification by other cellular proteins. Here, we discuss the exciting progress that has recently been made in deciphering the regulation of the NLRP3 inflammasome. Additionally, we highlight open questions and describe areas of research that warrant further exploration to obtain a more comprehensive molecular and cellular understanding of the NLRP3 inflammasome.

Chlorogenic Acid Suppresses miR-155 and Ameliorates Ulcerative Colitis through the NF-κB/NLRP3 Inflammasome Pathway

SCOPE

The over-activation of the nucleotide-binding domain like receptor protein 3 (NLRP3) inflammasome plays an important role in the pathogenesis of ulcerative colitis (UC). Chlorogenic acid (CGA) exposure is identified as an effective strategy for repressing inflammatory responses.

METHODS AND RESULTS

In this study, the NLRP3 inflammasome model with LPS/ATP-induced RAW264.7 cells in vitro and dextran-sulfate-sodium (DSS)-induced colitis in mice are used to evaluate the effect of CGA on NLRP3 inflammasome-related signaling. The results suggest that CGA suppressed the expression of NLRP3 inflammasome-related genes (apoptosis-associated speck-like protein containing CARD (ASC), cysteine-requiring aspartate protease (Caspase)-1 p45, Caspase-1 p20, pro-/cleaved-interleukin (IL)-1β, pro-/cleaved-IL-18), p-nuclear factor kappa B (NF-κB) protein, and miR-155 in mice with colitis. Gain- and loss-of-function studies of miR-155 are performed to elucidate its role in inflammation. Moreover, activation of the NF-κB/NLRP3 inflammasome pathway and miR-155 expression is investigated. CGA exposure in lipopolysaccharide (LPS)/adenosine triphosphate (ATP)-stimulated RAW264.7 cells leads to a decrease in p-NK-κB and NLRP3 inflammasome-related proteins, which is dependent on the downregulation of miR-155 expression.

CONCLUSIONS

These findings indicate that CGA prevented colitis by downregulating miR-155 expression and inactivating the NF-κB/NLRP3 inflammasome pathway in macrophages. The current study has promising therapeutic implications in the treatment of UC.